Method for determining the efficiency of a vaporizer in a decontamination system

ABSTRACT

An apparatus for determining the efficiency of a vaporizer in a decontamination system, having a first sensor for generating a first signal indicative of the concentration of a decontaminating chemical in a liquid decontaminate before vaporization by a vaporizer, and a second sensor for generating a second signal indicative of the concentration of vaporized decontaminate after vaporization by said vaporizer, and means for determining efficiency in accordance with said first and second signal.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/844,468, filed May 12, 2004.

FIELD OF THE INVENTION

The present invention relates generally to a decontamination process,and more particularly to a method and apparatus for determining theefficiency of a vaporization system for a decontamination system.

BACKGROUND OF THE INVENTION

Vaporization systems are used in decontamination systems to producegases such as vaporized hydrogen peroxide. As used herein, the term“decontamination” refers to processes, including, but not limited to,“deactivation of biocontamination,” “deactivation of chemicalcontamination,” “sterilization,” “disinfection” and “sanitization.” Inthe case of a typical hydrogen peroxide decontamination system, anaqueous solution of hydrogen peroxide is delivered to a vaporizer wherethe aqueous solution of hydrogen peroxide is vaporized. The resultingmixture of vaporized hydrogen peroxide and water vapor is then injectedinto a treatment chamber, where articles are decontaminated by exposureto the vaporized hydrogen peroxide.

Efficient vaporization of the aqueous solution of hydrogen peroxide isimportant to the effective operation of a decontamination system usingvaporized hydrogen peroxide. The aqueous solution of hydrogen peroxideis typically comprised of liquid hydrogen peroxide diluted with water.When solutions are vaporized, a disproportionate amount of the morevolatile component will vaporize first. In the case of theabovementioned aqueous solution of hydrogen peroxide, water is morevolatile than hydrogen peroxide and therefore vaporizes more quicklythan the liquid hydrogen peroxide. Thus, the water vapor reaches thearticles in the treatment chamber to be decontaminated before thehydrogen peroxide vapor, and in higher concentrations. Consequently, thewater vapor becomes an effective barrier to hydrogen peroxidepenetration around small crevices and lumens of the articles in thetreatment chamber.

In view of the aforementioned problem, decontamination systems have beendeveloped that vaporize an aqueous solution of hydrogen peroxide byinjecting the aqueous solution of hydrogen peroxide into a vaporizationchamber, wherein successive increments of the aqueous solution ofhydrogen peroxide are metered onto a heated surface inside thevaporization chamber. Each increment of the aqueous solution of hydrogenperoxide is substantially instantaneously vaporized before the nextsucceeding increment of the aqueous solution hydrogen peroxide ismetered onto the heated surface.

One problem with such systems is that over time the concentration ofvaporized hydrogen peroxide within the system may not reach desiredlevels because the efficiency level of the vaporizer may have decreased.Efficient vaporization of an aqueous solution of hydrogen peroxidedepends upon substantially instantaneous vaporization of an increment ofthe aqueous solution of hydrogen peroxide. When an increment of theaqueous solution of hydrogen peroxide does not substantiallyinstantaneously vaporize, the efficiency of the vaporizer decreases.Such a decrease in efficiency may occur because deposits develop onsurfaces that contact and transmit heat to the aqueous solution ofhydrogen peroxide. The decreased efficiency will result in lower thandesired concentrations of vaporized hydrogen peroxide within thedecontamination system. A reduction in the concentration of vaporizedhydrogen peroxide within the system may result in reduced efficacy ofdecontamination or increased decontamination times.

The present invention provides an apparatus and a method for determiningthe efficiency of a vaporizer in a decontamination system.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention,there is provided an apparatus for determining the efficiency of avaporizer in a decontamination system, comprising: (a) a first sensorfor generating a first signal indicative of the concentration of adecontaminating chemical in a liquid decontaminate before vaporizationby a vaporizer; (b) a second sensor for generating a second signalindicative of the concentration of vaporized decontaminate aftervaporization of the liquid decontaminate by said vaporizer; and (c)means for determining efficiency in accordance with said first andsecond signals.

In accordance with another aspect of the invention, there is provided amethod for determining efficiency of a vaporizer for a vaporizationprocess, the method comprising the steps of: (a) exposing a liquiddecontaminate including a decontaminating chemical to a first sensor todetermine the concentration of the decontaminating chemical in theliquid decontaminate; (b) vaporizing the liquid to produce a gasincluding a vaporized decontaminate; and (c) exposing the gas to asecond sensor to determine the concentration of the vaporizeddecontaminate.

In accordance with yet another aspect of the present invention, there isprovided a method for determining a vaporization efficiency of avaporizer in a decontamination system, the method comprising the stepsof: (a) exposing a first sensor to a liquid, said liquid being comprisedof a decontaminating chemical and at least one other component, whereinsaid liquid is supplied to a vaporizer; (b) vaporizing said liquid insaid vaporizer to generate a gas; (c) exposing a second sensor to saidgas, said gas being comprised of a vaporized decontaminate and at leastone other component; (d) determining a concentration of decontaminatingchemical in said liquid; and (e) determining a concentration ofdecontaminate in said gas.

An advantage of the present invention is the provision of a method andapparatus for determining the efficiency of vaporization for a vaporizerused in connection with a decontamination system.

Another advantage of the present invention is the provision of a methodand apparatus for comparing the efficiency of vaporization to a baseline efficiency of vaporization.

These and other objects will become apparent from the followingdescription of a preferred embodiment taken together with theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, a preferred embodiment of which will be described in detail inthe specification and illustrated in the accompanying drawings whichform a part hereof, and wherein:

FIG. 1 is a schematic view of an exemplary vaporized hydrogen peroxidedecontamination system including an apparatus for determining theefficiency of vaporization according to a preferred embodiment of thepresent invention;

FIG. 2 is a block diagram of an exemplary sensor for determining theconcentration of a liquid chemical, according to a first embodiment;

FIG. 3 is a schematic diagram of the sensor system of FIG. 2;

FIG. 4 is a schematic diagram of an exemplary sensor for determining theconcentration of a liquid chemical, according to a second embodiment;

FIG. 5 is a schematic diagram of an exemplary sensor for determining theconcentration of a liquid chemical, according to a third embodiment;

FIG. 6 is a top, plan view of an exemplary sensor for determining theconcentration of a gaseous chemical, according to a preferredembodiment;

FIG. 7 is a side, elevation view of the sensor shown in FIG. 6;

FIG. 8 is an exploded view of the sensor shown in FIG. 6; and

FIG. 9 is a flow chart of a method for determining the efficiency ofvaporization for hydrogen peroxide, according to a preferred embodimentof the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating the invention only, and not for the purpose of limitingsame, FIG. 1 shows an exemplary decontamination system 10.Decontamination system 10 is generally comprised of a liquiddecontaminate supply 52, a pump 62, a vaporizer 30, a room or housing 22that defines a region or treatment chamber 24, a system controller 98, aliquid concentration sensor 100, and a vapor concentration sensor 200.Decontamination system 10 is an “open loop” system. It should beunderstood that the present invention is also suitably used inconnection with a “closed loop” system.

In the embodiment shown, liquid decontaminate supply 52 provides aliquid decontaminate through feed line 54 to pump 62. It is recognizedthat the liquid decontaminate may be comprised of one or more liquiddecontaminating chemicals, or one or more liquid decontaminatingchemicals in combination with one or more chemicals that are notdecontaminating chemicals. In the illustrated embodiment, the liquiddecontaminate provided by liquid decontaminate supply 52 is an aqueoussolution of hydrogen peroxide. Pump 62 is driven by a motor (not shown)and is provided to convey metered amounts of the liquid decontaminate tovaporizer 30 from liquid decontaminate supply 52.

Vaporizer 30 is a vaporizer as is conventionally known for thevaporization of liquid decontaminates. Vaporizer 30 vaporizes the liquiddecontaminate using a conventionally known heating element 32. Heatingelement 32 has evaporation surfaces operable to vaporize metered amountsof liquid decontaminate. The vaporized components of the liquiddecontaminate exit vaporizer 30 through supply conduit 42, and entertreatment chamber 24 through inlet port 44.

In a preferred embodiment, system controller 98 is a microprocessor,microcontroller, processor, processing unit, or like device programmedto control the operation of system 10. As illustrated in FIG. 1, systemcontroller 98 is connected to an output unit 99 and a memory 96. Outputunit 99 provides information to the operator in an audible and/or visualform. Accordingly, output unit 99 may take the form of an audio speakerand/or a visual display unit. Memory 96 provides data storagecapabilities for system controller 98. Additionally, system controller98 is electrically connected to liquid concentration sensor 100 andvapor concentration sensor 200.

In the illustrated embodiment, system 10 is a decontamination system fordecontaminating objects with hydrogen peroxide, and more particularly,with vaporized hydrogen peroxide. Accordingly, liquid concentrationsensor 100 and vapor concentration sensor 200 shall be described withrespect to determining the concentration of hydrogen peroxide in anaqueous solution, and as a part of a two-component, vapor-phase mixturewhere water vapor is a second component.

In the illustrated embodiment, liquid concentration sensor 100 is of thetype described in U.S. application Ser. No. 10/389,036, filed Mar. 14,2003, entitled “Method and Apparatus for Measuring ChemicalConcentration in a Fluid,” which is fully incorporated herein byreference, and described further below.

Referring now to FIG. 2, there is shown a block diagram of an exemplaryliquid concentration sensor 100 according to a first embodiment. Sensor100 senses the concentration of chemicals in a solution generally, andin a preferred embodiment, senses the concentration of chemicals in aliquid decontaminate (e.g., an aqueous solution of hydrogen peroxide) byuse of a capacitor, as will be described in detail below. FIG. 3provides a detailed schematic of sensor 100 according to the firstembodiment. In this embodiment, sensor 100 takes the form of a “bridgecircuit.” As is well known to those skilled in the art, bridge circuitsare used to determine the value of an unknown impedance in terms ofother impedances of known value. Highly accurate measurements arepossible because a null condition is used to determine the unknownimpedance. The bridge circuit is used to determine a capacitance valueindicative of the concentration of chemicals in a liquid decontaminate(e.g., an aqueous solution of hydrogen peroxide). Sensor 100 isgenerally comprised of a voltage source 122 that acts as a signalgenerator, a null detector 130, an electronic potentiometer 140, acapacitor 108 of known capacitance C₁, and a capacitor 110 ofcapacitance C_(x). Sensor 100 is electrically connected to systemcontroller 98 to communicate electrical signals therebetween, as will bedescribed below (See FIG. 1).

Capacitor 110 acts as a sensing element, and is directly exposed to theliquid decontaminate in feed line 54 as shown in FIG. 1. In oneembodiment, capacitor 110 is a parallel plate capacitor. However, itshould be appreciated that capacitor 110 could be constructed in adifferent form. For example, capacitor 110 could be a cylindrical orspherical capacitor. If a spherical capacitor is used as capacitor 110,holes must be placed in the outer shell of the capacitor such thatliquid decontaminate can enter and exit the capacitor.

As stated above, in a preferred embodiment of the present invention, theliquid decontaminate is an aqueous solution of hydrogen peroxide.Therefore, in a preferred embodiment, capacitor 110 is directly exposedto an aqueous solution of hydrogen peroxide. Capacitor 110 is preferablydisposed within feed line 54 in such a way that the liquid decontaminatein feed line 54 fills the gap between the conducting plates of capacitor110, thereby acting as the insulator or “dielectric” of capacitor 110.Sensor 100 provides data indicative of a capacitance C_(x),corresponding to a chemical concentration. In this regard, capacitanceC_(x) will vary in accordance with the concentration of chemicalcomponents in the liquid decontaminate.

It should be appreciated that capacitor 110 may be alternativelydisposed in such a way as to sense chemical concentrations within liquiddecontaminate supply 52, or at any location within vaporizer 30 whereliquid decontaminate may be present.

Referring now to FIG. 2, electronic potentiometer 140 functions in thesame manner as a mechanical potentiometer. In this regard, electronicpotentiometer 140 is a three terminal device. Between two of theterminals is a resistive element. The third terminal, known as the“wiper,” is connected to various points along the resistive element. Ina preferred embodiment, the wiper is digitally controlled by systemcontroller 98 (see FIG. 1). It is appreciated that the wiper could becontrolled by a controller other than controller 98. The wiper dividesthe resistive element into two resistors R_(BC) and R_(AC). Electronicpotentiometer 140 may take the form of a digitally programmablepotentiometer (DPP™) available from Catalyst Semiconductor, Inc. ofSunnyvale, Calif.

Voltage source 122 provides an AC voltage signal, such as a sinusoidalor pulse waveform. Null detector 130 is a device for detecting a nullcondition (i.e., a short circuit), such as a galvanometer, a voltmeter,a frequency-selective amplifier, and the like.

Operation of sensor 100, as shown in FIG. 3, will now be described indetail. The elements of the bridge circuit are connected betweenjunctions AC, BC, AD, and BD. Electronic potentiometer 140 is operatedby system controller 98 to vary the resistances R_(BC) and R_(AC) untilthe potential difference between junctions A and B (V_(AB)) is zero.When this situation exists, the bridge is said to be balanced or is“nulled.” The following relationships then hold for voltages in the mainbranches:V_(AC)=V_(BC), and V_(AD)=V_(BD),where V_(AC) is the voltage between junctions A and C, V_(BC) is thevoltage between junctions B and C, V_(AD) is the voltage betweenjunctions A and D, and V_(BD) is the voltage between junctions B and D.Accordingly,V _(AD) /V _(AC) =V _(BD) /V _(BC)V _(AD) =V _(BD)/(V _(AC) /V _(BC))

Capacitor 110, having capacitance C_(x), is connected between junctionsA and D, and capacitor 108, having capacitance C₁, is connected betweenjunctions B and D. Electronic potentiometer 140, connected from junctionA to junction C to junction B, is adjusted by system controller 98 tovary the voltages V_(AC) and V_(BC).

When a null is detected by null detector 130, current I₁ flows fromjunction C to junction A to junction D, and a current I₂ flows fromjunction C to junction B to junction D. The voltage V_(AC) acrossjunctions A to C, and the voltage V_(BC) across junctions B to C are:V_(AC)=I₁R_(AC) and V_(BC)=I₂R_(BC).

The voltage across a capacitor with capacitance C, current I, andfrequency is:

$V = \frac{I}{2\;\pi\;{fC}}$

Therefore, the voltages V_(AD) and V_(BD) may be expressed as:

$V_{AD} = \frac{I_{1}}{2\;\pi\;{fC}_{x}}$$V_{BD} = \frac{I_{2}}{2\;\pi\;{fC}_{1}}$

As discussed above, V_(AD)=V_(BD)/(V_(AC)/V_(BC)), V_(AC)=I₁R_(AC) andV_(BC)=I₂R_(BC). Therefore,

$C_{x} = {{C_{1}( \frac{R_{BC}}{R_{AC}} )}.}$

In view of the foregoing relationship, when a null condition isdetected, the resistance values for R_(BC) and R_(AC), along with theknown capacitance value C₁, of capacitor 108, can be used to determineunknown value of capacitance C_(x) of capacitor 110.

Sensor 100 utilizes differences in dipole moments of different moleculesto determine the concentration of a chemical in a liquid decontaminate.As discussed above and shown in FIG. 1 liquid decontaminate travelingthrough feed line 54 fills the gap between the conducting plates ofcapacitor 110, thereby acting as the dielectric of capacitor 110. Byconfiguring capacitor 110 as an element of a bridge circuit, a measureof resistance values R_(AC) and R_(BC), when the bridge is balanced ornulled, can be used to determine capacitance C_(x) of capacitor 110.Capacitance C_(x) is indicative of the concentrations of the chemicalcomponents in the liquid decontaminate, since the permittivity of therespective dielectric is affected by the concentrations of the chemicalcomponents of the liquid decontaminate.

It should be appreciated that while the illustrated embodiment of sensor100 takes the form of a bridge circuit, other types of circuits andtechniques (including other types of bridge circuits, and capacitancemeters) known to those skilled in the art, may be suitably used tomeasure capacitance. For example, FIG. 4 illustrates an alternativesensor 100A. Sensor 100A is an LC resonant circuit, having a variablecapacitor C_(A) and a capacitor 110 having a capacitance C_(x) directlyexposed to the liquid decontaminate in feed line 54. In this regard, theliquid decontaminate fills the gap between the conducting plates ofcapacitor 110, thereby acting as the insulator or “dielectric” ofcapacitor 110. Since the resonance frequency ω₀=[L(C_(A)+C_(x))]^(−1/2),the unknown capacitance of capacitor 110 can be determined.

FIG. 5 illustrates yet another alternative liquid concentration sensor100B suitable for use in connection with the present invention. In thisembodiment, liquid concentration sensor 100B is a “charge transfer”sensor circuit. Charge transfer sensor circuits are recognized toprovide resolutions of fractions of a femtoFarad. In a charge transfersensor circuit the unknown capacitance C_(x) of capacitor 110 isdetermined by charging the sense electrode to a fixed potential, andthen transferring that charge to a charge detector comprising acapacitor 118 of known capacitance C_(A). Liquid decontaminate fills thegap between the conducting plates of capacitor 110 of liquidconcentration sensor 100B, thereby acting as an insulator or“dielectric” of capacitor 110. Capacitor 110 is first connected to a DCreference voltage (V_(r)) via a switch S₁. Switch S₁ is reopened aftercapacitor 110 is satisfactorily charged to the potential of V_(r). Then,after as brief as possible a delay so as to minimize leakage effectscaused by conductance, switch S₂ is closed and the charge (Q) present oncapacitor 110 is transferred to capacitor 118 (i.e., the chargedetector). Once the charge Q is satisfactorily transferred to capacitor118, switch S₂ is reopened. By reading voltage V_(s), the capacitanceC_(x) of capacitor 110 can be determined. V_(s) may be input to anamplifier to provide the scaling necessary to present ananalog-to-digital converter (ADC) with a useful range of voltage fordigital processing. Switch S₃ acts as a reset means to reset the chargebetween charge transfer cycles, so that each charge transfer cycle has aconsistent initial condition. Switches S₁, S₂ and S₃ may beelectromechanical switches or transistors. Preferably, digital controllogic is used to control switches S₁, S₂ and S₃. In a preferredembodiment, capacitor 118 is selected to have significantly morecapacitance than capacitor 110.

The equations governing this alternative embodiment are as follows:V _(s) =V _(r) [C _(x)/(C _(x) +C _(A))], thereforeC _(x) =V _(s) C _(A) /[V _(r) −V _(s)].

It is recognized that in some cases, the capacitance of the capacitorexposed to the liquid decontaminate located in feed line 54 may be inthe range of femtoFarad capacitance to low picoFarad capacitance (e.g.,1 fF to 100 pF), and that changes in concentration of a chemical in theliquid decontaminate may only result in a change of capacitance in therange of low picoFarad capacitance or even femtoFarad capacitances.Accordingly, the sensor circuit used to measure capacitance may need tohave high sensitivity to allow for measurement of small values ofcapacitance. One high sensitivity sensor circuit is the charge transfersensor circuit described above. Other high sensitivity circuitry isprovided by such devices as the PTL 110 capacitance transducer fromProcess Tomography Limited of Cheshire, United Kingdom. The PTL 110measures small values of capacitance (up to 10 picoFarads) with aresolution of 1 femtoFarad. A 1616 Precision Capacitance Bridge from IETLabs, Inc. of Westbury, N.Y., allows for measurement of capacitances inthe range from 10-7 pF to 10 μF. Tektronix produces the Tektronix 130 LCMeter that measures capacitance from 0.3 pF to 3 pF. It has also beenacknowledged in the prior art literature that capacitance sensorcircuits using modern operational amplifiers and analog-to-digitalconverters (ADCs) can easily obtain resolutions to 0.01 pF.

With reference to FIGS. 1-3, operation of sensor 100, according to apreferred embodiment, will now be described in detail. As a preliminarystep, system controller 98 stores in memory 96 a set of data comprisingvalues of the capacitance of capacitor 110 having a capacitance C_(x)for a plurality of concentrations of a liquid decontaminate. This set ofdata may be determined by exposing capacitor 110 of sensor 100 toseveral different combinations of concentrations of a decontaminatingchemical in the liquid decontaminate, and recording the correspondingmeasured capacitance C_(x). For example, system controller 98 may storevalues of the capacitance C_(x) of capacitor 110 that are determined fora plurality of concentrations of a liquid decontaminate comprised ofonly two components. As the concentrations of the first and secondcomponents are varied, the corresponding capacitance of capacitor 110 isdetermined and stored in memory 96. For instance, capacitance ofcapacitor 110 may be determined for various concentrations of a firstcomponent and a second component (at a fixed volume of the liquiddecontaminate), including, but not limited to:

0% first component and 100% second component,

25% first component and 75% second component,

50% first component and 50% second component,

75% first component and 25% second component, and

100% first component and 0% second component.

After the set of data is stored in memory 96, measurement ofconcentrations of a decontaminating chemical in a liquid decontaminatecan commence. Capacitor 110 is exposed to a liquid decontaminate in feedline 54. As indicated above, capacitor 110 may be located in liquiddecontaminate supply 52, any location within vaporizer 30 where liquiddecontaminate may be present, or any other location where capacitor 110will be exposed to liquid decontaminate. A determination of R_(AC) andR_(BC) when the bridge is nulled is then used to determine a value forthe capacitance of capacitor 110. As discussed above,C_(x)=C₁(R_(BC)/R_(AC)). The data stored in memory 96 is searched forthe capacitance C_(x) of capacitor 110 to obtain the correspondingconcentrations. A linear relationship between concentration andcapacitance allows one to normalize any measurement made so as toprovide the concentration of each component in the solution. If thecapacitance C_(x) of capacitor 110 is not found in the pre-stored data,the stored data may be interpolated or extrapolated to obtain aconcentration corresponding to the measure capacitance of capacitor 110.As noted above, frequency of the waveform generated by voltage source122 will influence the response of capacitors. Where the capacitanceC_(x) of capacitor 110 does not exhibit a suitable linear response, anexpanded set of data points should be stored in memory 96, so thatinterpolation or extrapolation is unnecessary.

It should be appreciated that while a preferred embodiment of thepresent invention uses a measure of a capacitor's capacitance todetermine concentrations, it is also contemplated that a measure ofother electrical properties of a capacitor may be used to determineconcentrations, including, but not limited to, the permittivity anddielectric constant of the capacitor dielectric.

In the illustrated embodiment, vapor concentration sensor 200 is of thetype described in U.S. application Ser. No. 10/663,593 filed Sep. 16,2003, entitled “Sensor for Determining Concentration of FluidSterilant,” which is fully incorporated herein by reference, anddescribed further below.

Referring now to FIGS. 6-8, vapor concentration sensor 200 is comprisedof a sensing element 212 having a layer or coating 262 of a materialthat interacts with, or is reactive with, the decontaminate used insystem 10, such that mechanical motion or movement of sensor 200 isconverted into an electrical signal and transmitted to system controller98.

Element 212 may be a moving or suspended component, but in a preferredembodiment, element 212 is a piezoelectric device, and more preferably,is a quartz crystal. Other piezoelectric materials, such as by way ofexample and not limitation, Rochelle salt, barium titanate, tourmaline,polyvinylidene fluoride and crystals that lack a center of symmetry arealso contemplated. In the embodiment shown, element 212 is a flat,circular quartz disk having a first planar, major surface 214 and asecond planar, major surface 216. An electrode 222 is disposed on thefirst major surface 214 and an electrode 232 is disposed optionally onthe second major surface 216.

Electrode 222 includes a main body portion 222 a that is centrallydisposed on first major surface 214 and a leg portion 222 b that extendsin a first direction to the edge of element 212. Similarly, electrode232 includes a main body portion 232 a that is centrally disposed onsecond major planar surface 216, and a leg portion 232 b that extends ina direction opposite to the first direction of leg portion 222 b,wherein leg portion 232 b extends to the edge of element 212. Main bodyportions 222 a, 232 a of electrodes 222, 232 are disposed respectivelyon first and second major surfaces 214, 216 to be aligned with eachother on opposite sides of element 212. Leg portions 222 b, 232 b extendin opposite directions from central body portions 222 a, 232 a, as bestseen in the drawings. Electrodes 222, 232 are deposited onto first andsecond planar surfaces 214, 216. Electrodes 222, 232 may be formed ofany electrically conductive material, but are preferably formed ofcopper, silver or gold. Electrical leads 242, 244 are attached to legportions 222 b, 232 b of electrodes 222, 232. Leads 242, 244 aresoldered, brazed or welded to electrodes 222, 232 to be in electricalcontact therewith.

At least one of the two major surfaces 214, 216 of element 212 is coatedwith a layer 262 of a material that interacts, or is reactive with, thedecontaminate to be used within system 10. In the embodiment shown,layer 262 is on major surface 214. In the embodiment shown, layer 262 isdefined by two arcuate or crescent-shaped layer areas 262 a, 262 b ofmaterial applied to first major surface 214 of element 212. Arcuatelayer areas 262 a, 262 b are disposed on first major surface 214 suchthat electrode 222 is disposed therebetween. The material forming layerareas 262 a, 262 b are preferably fixedly attached to surface 214 ofelement 212. The mass of the material on element 212 is dependent uponthe desired performance characteristics of vapor concentration sensor200. As indicated above, the material forming layer areas 262 a, 262 bis preferably one that interacts or reacts with the decontaminate usedwithin system 10.

In the illustrated embodiment, the decontaminate to be detected by vaporconcentration sensor 200 is vaporized hydrogen peroxide, and thematerial that forms layer areas 262 a, 262 b on first major surface 214of vapor concentration sensor 200 is a metal oxide, namely, lead dioxide(PbO₂). It is believed that other metal oxides having various states,such as silver (II) oxide (AgO) or manganese (IV) oxide (MnO₂), may beused. It is also contemplated that metal oxides having mixed valencystates, such as by way of example and not limitation, a metal oxidehaving a mixture of single and divalent oxide states may be used.

In the illustrated embodiment, sensor 200 is disposed within supplyconduit 42 and is connected to system controller 98 as shown in FIG. 1,to provide electrical signals thereto. It should be understood thatsensor 200 may be alternatively disposed in such a way as to sense theconcentration of vaporized hydrogen peroxide within treatment chamber 24or within vaporizer 30.

System controller 98 includes an oscillating circuit (not shown) that isconnected to sensor 200 to convert movement of sensor 200 intoelectrical signals, as is conventionally known. System controller 98also includes stored data indicative of the electrical responses ofsensor 200 to predetermined concentrations of a decontaminate to besensed. In the embodiment heretofore described, where sensor 200 is aquartz crystal and layer areas 262 a, 262 b are lead dioxide, the datarelating to sensor 200 that is stored within system controller 98 isempirical data accumulated under controlled, laboratory conditions.

The empirical data relating to sensor 200 that is stored in systemcontroller 98 may be acquired as follows. The natural frequency of aquartz crystal (without a coating thereon) is measured. The lead dioxideis applied to the quartz crystal and the mass of the coating isdetermined using the Sauerbre equation. The quartz crystal is thenexposed to various, controlled concentrations of vaporized hydrogenperoxide. A graph of the change in frequency per unit mass of coating(or, using the Sauerbre equation, the change in weight per unit mass ofcoating) versus concentration of decontaminate or oxidant is producedand stored in a data storage device within system controller 98.Alternatively, the data could be stored not as a graph but rather inlook-up tables. As will be appreciated, if a coating of uniformthickness is applied to a crystal, the change in frequency or weightcould be normalized on a per unit surface area basis.

As suggested, in one embodiment, the change in frequency or weight isdivided by the mass of the coating applied to the quartz crystal so thatregardless of the mass of coatings applied to other crystals, the changein frequency will be normalized to a unit mass of the coating. Datataken with other quartz crystals that may have coatings of differentamounts of mass than the laboratory crystal can still be compared to thestored data obtained from the laboratory crystal as both sets of datawill be normalized to a change in frequency or weight per unit mass ofthe coating. It will be appreciated that with modern deposition means,it may not be necessary to normalize the data as coatings with littlephysical variation can be deposited from one crystal to the next.

In another embodiment, a quartz crystal is coated with lead oxide and isthen exposed to known concentrations of vaporized hydrogen peroxide soas to develop a set of data, or a curve, of equilibrium frequencyreduction values as a function of concentration of vaporized hydrogenperoxide for the quartz crystal. The coated quartz crystal is theninstalled in system 10. The associated set of data, or curve, isprogrammed or stored in memory 96 of system controller 98. Thus, thedata stored in system controller 98 matches the crystal sensor withinvapor concentration sensor 200, thereby providing a standardized system.In this manner, vapor concentration sensor 200 has a coated quartzcrystal sensor with an associated standardized data set stored withinmemory 96, as the stored data set was produced by exposing that specificquartz crystal to known concentrations of vaporized hydrogen peroxide.

Vapor concentration sensor 200 operates based upon the concept that thefrequency of a piezoelectric device will change in relation to a changein mass of a layer on the device, as a result of exposure to vaporizedhydrogen peroxide.

Specifically, the frequency of a piezoelectric device is related to themass change, as determined by the Sauerbre equation:Δf=−(C _(f))(Δm)Δf=−(f _(o) ² /Nρ)Δm

where:

-   -   Δf is the frequency change    -   Δm is the mass change per unit area on the surface of the        piezoelectric device    -   C_(f) is a sensitivity constant    -   f_(o) is the operating frequency of the piezoelectric device        prior to the mass change    -   N is the frequency constant for the piezoelectric device    -   ρ is the density of the piezoelectric device

It should be appreciated that sensor 200 may be disposed within system10 in such a way that best senses the surrounding vapor. Various methodsfor installing sensors in flowing fluids will be recognized by oneskilled in the art. By way of example and not limitation, these includescreens, changes in conduit diameter, stilling wells and other methodsto expose a sensor to a fluid such as a liquid decontaminate or a vaporfor the appropriate amount of time with the appropriate amount ofcontact.

It should be understood that liquid concentration sensor 100 and vaporconcentration sensor 200 as described in connection with the illustratedembodiment of the present invention are only exemplary sensors, and arenot intended to limit the scope of the present invention. In thisregard, it is contemplated that sensors 100 and 200 may be selected fromany suitable sensors known to one skilled in the art. For instance,sensor 200, as described above, may also be suitable for use indetecting concentrations in a liquid, and thus may be substituted forsensor 100. Furthermore, vapor concentration sensor 200 could be of thetype described in U.S. application Ser. No. 10/405,880, filed Apr. 2,2003, entitled “Method and Apparatus for Measuring Concentration of aChemical Component in a Gas Mixture,” which is fully incorporated hereinby reference. Furthermore, sensors 100, 100A and 100B, as describedabove, may also be suitable for use in detecting concentrations in avapor, and thus may be substituted for sensor 200.

The present invention shall now be further described with reference tothe operation of system 10. In a preferred embodiment, pump 62 dispensesan aqueous solution of hydrogen peroxide into vaporizer 30 where theaqueous solution of hydrogen peroxide is vaporized. The vaporizedhydrogen peroxide and vaporized water pass through supply conduit 42into treatment chamber 24 where articles to be sterilized ordecontaminated are disposed. Vaporized hydrogen peroxide is supplied totreatment chamber 24 in amounts sufficient to effect decontamination ofthe articles disposed therein.

Over time, the effectiveness of a decontamination cycle as described bythe foregoing may decrease due to a reduced vaporization efficiency ofvaporizer 30. The reduction in vaporization efficiency of vaporizer 30may occur when evaporation surfaces such as those of heating element 32within vaporizer 30 develop contamination or scale buildup that reducesthe efficiency of heat transfer. As the heat transferred is reduced, therate of vaporization also decreases. The rate of vaporization should besubstantially instantaneous for a vaporizer 30 to function correctly. Ifvaporization is not substantially instantaneous, puddles of unevaporatedaqueous solution of hydrogen peroxide may accumulate within thevaporizer. When such puddles accumulate, vaporization becomes dependentupon the relative partial pressures of the components of thedecontaminate.

By way of example and not limitation, in the embodiment shown, theaqueous solution of hydrogen peroxide supplied to vaporizer 30 istypically comprised of about 65% water and about 35% hydrogen peroxide(by weight). If such a solution were substantially instantaneouslyvaporized, the proportions of hydrogen peroxide and water in the vaporwould also be about 65% water and about 35% hydrogen peroxide. However,if such a solution were not substantially instantaneously vaporized,preferential boiling due to the differing vapor pressures of water andhydrogen peroxide would result in a vapor concentration of water inexcess of 65%. The concentration of hydrogen peroxide in the vapor fromvaporizer 30 would therefore be less than 35%.

Vaporization efficiency can function as a metric to be used for theidentification of vaporization problems that may affect sterilization.For example, a decrease of the vaporization efficiency over timeindicates that the concentration of hydrogen peroxide in the vaporleaving vaporizer 30 is less than the concentration of the hydrogenperoxide in the aqueous solution entering vaporizer 30 from feed line54. In such a situation, an operator could be notified that vaporizer 30is in need of cleaning.

An advantage of using vaporization efficiency as a metric is that it canprovide automatic monitoring of the operation of vaporizer 30 withoutthe need for direct physical inspection of vaporizer 30. Anotheradvantage is that fluctuations of the concentration of vaporizedhydrogen peroxide that are a result of fluctuations of the concentrationof hydrogen peroxide in the aqueous solution of hydrogen peroxide infeed line 54 may be compensated for by appropriate timing of dataacquisition, as will be discussed further below.

As used herein, an “efficiency of vaporization” is used to express theconcentrations of hydrogen peroxide in a liquid solution and in a vaporresulting from that solution. In the embodiment shown, the efficiency ofvaporization of vaporizer 30 is monitored by system controller 98. It isappreciated that the efficiency of vaporization may be monitoredcontinuously or periodically during a given cycle or a given phase of acycle (e.g., the decontamination phase), as necessary, to ensure thatvaporizer 30 is in proper working order.

In order to describe the efficiency of vaporization as used to monitorand describe the condition of vaporizer 30 and the effectiveness ofsystem 10, it is necessary to define terms that will be used to furtherdescribe the method for determining the vaporization efficiency of asterilizer.

As used herein, the term “actual vaporization efficiency” refers to theconcentration of hydrogen peroxide in the vapor divided by theconcentration of hydrogen peroxide in the aqueous solution beingsupplied to vaporizer 30.

As used herein, the term “baseline vaporization efficiency” refers to an“actual vaporization efficiency” determined at some point in time forlater use as a benchmark to determine the performance of the vaporizer.

As used herein, the term “effective vaporization efficiency” refers tothe ratio of “actual vaporization efficiency” to “baseline vaporizationefficiency.” The effective vaporization efficiency may be used toevaluate the performance of various systems 10 or of a given system 10with different vaporizers 30.

In a preferred embodiment, given perfect conditions and assuming nodecomposition of hydrogen peroxide prior to vapor concentration sensor200, the actual vaporization efficiency would be 100%. The actualvaporization efficiency is determined by dividing the concentration ofhydrogen peroxide in the vapor produced by vaporizer 30 (e.g., 35%) bythe concentration of hydrogen peroxide of the aqueous solution ofhydrogen peroxide provided to vaporizer 30 (e.g., 35%).

It is contemplated that on initial startup and qualification of a system10, the actual vaporization efficiency of vaporizer 30 may not be 100%.Therefore in a preferred embodiment, the baseline vaporizationefficiency is determined prior to installation and regular use of system10. The baseline vaporization efficiency can be used as a basis forcomparison with the actual vaporization efficiency to determine whetherthe rate of heat transfer and therefore scale buildup within vaporizer30 has changed such that maintenance of vaporizer 30 or replacement ofvaporizer 30 is required.

It is further contemplated that baseline vaporization efficiency may bedirectly compared with an actual vaporization efficiency in order todetermine the decontamination effectiveness of system 10. Such acomparison would be effective when sensor 200 is disposed in a locationor a manner such that the hydrogen peroxide concentration in the vaporis not affected by factors other than vaporization efficiency.

A mathematical method for comparing the baseline vaporization efficiencywith the actual vaporization efficiency is the calculation of effectivevaporization efficiency. Effective vaporization efficiency is determinedby dividing the actual vaporization efficiency by baseline vaporizationefficiency. During operation of system 10, the effective vaporizationefficiency may be monitored by system controller 98 to determine thecurrent effectiveness of vaporizer 30 within system 10. Vaporizer 30 canbe refurbished, cleaned, or otherwise brought into acceptable conditionwhen the effective vaporization efficiency drops below the desiredlevel. The minimum desired level of effective vaporization efficiency isdetermined prior to operation of system 10.

A method of determining the efficiency in a decontamination system willnow be described in accordance with a preferred embodiment of thepresent invention, as shown in FIG. 1. As illustrated in FIG. 1, sensingelement 110 is disposed within feed line 54 and vapor concentrationsensor 200 is disposed within supply conduit 42.

Referring now to FIG. 9, there is shown a method 70 for determiningvaporization efficiency for vaporizer 30. Liquid concentration sensor100 provides data indicative of the hydrogen peroxide concentrationX_(L) to system controller 98 in step 74. Similarly, vapor concentrationsensor 200 provides data indicative of the concentration of vaporizedhydrogen peroxide, X_(V), to system controller 98 in step 72.

It is appreciated that X_(L) and X_(V) represent concentrations ofhydrogen peroxide in the liquid decontaminate and the vapor mixture tobe sampled at a given moment in time and at a given place, and mayfluctuate for various reasons other than the operation of vaporizer 30.Therefore, it may be desirable to calculate the actual vaporizationefficiency E_(A) using values of X_(L) and X_(V) that generallyrepresent the concentrations of a particular unit mass of thedecontaminate to be sampled in both the liquid decontaminate and thevapor mixture. In this way variations of BA due to reasons other thanthe operation of the vaporizer 30 would be reduced. Thus, fluctuationsof E_(A) would be more attributable to the operation of vaporizer 30.

System controller 98 determines the actual vaporization efficiency E_(A)using values X_(V) and X_(L). As shown in step 76 of FIG. 9;

$\frac{X_{v}}{X_{L}} = E_{A}$

In step 82, actual vaporization efficiency E_(A) is compared to baseline efficiency E_(BL) obtained from storage or input (step 78), and aneffective vaporization efficiency E_(EFF) is calculated.

$E_{EFF} = \frac{E_{A}}{E_{BL}}$

The baseline vaporization efficiency of E_(BL) may be entered and/orstored in system controller 98 as a single value or may be part of adata table stored within system controller 98. The effective minimumefficiency may also be entered and/or stored in controller 98.

In step 84, the effective vaporization efficiency E_(EFF) is compared topredetermined threshold values/ranges to determine whether E_(EFF) iswithin an acceptable range. The predetermined values may be stored insystem controller 98. Step 84 may take place electronically withinsystem controller 98 or step 84 may be conducted manually.

If the effective vaporization efficiency E_(EFF) is within an acceptablerange, the operation of decontamination continues as normal, as shown instep 88. If the effective vaporization efficiency is not within theacceptable range, the operator may be alerted to the condition byaudible or visible indicators. The operator may then take correctiveaction as shown in step 86 in FIG. 9 that may include extension of thecurrent decontamination cycle in order to effectively sterilize orinsure an effective decontamination of the device as disposed withinsystem 10. Alternatively, the decontamination cycle may be stoppedimmediately and vaporizer 30 may be replaced or maintained in a mannersuch that it can vaporize with an acceptable effective vaporizationefficiency E_(EFF). As another alternative, the decontamination cyclemay be continued to the end and maintenance performed on vaporizer 30 atthe completion thereof. If necessary, vaporizer 30 may be replaced asnecessary.

The present invention shall now be further described with respect tovarious hypothetical vaporization efficiencies are determined forvarious given concentrations of hydrogen peroxide.

EXAMPLE

HYPOTHETICAL VAPORIZATION EFFICIENCIES TABLE X_(L) (conc. of liquidhydrogen peroxide) 34% 34% X_(V) (conc. of vaporized hydrogen peroxide)34% 30% ${E_{A}({calc})} = \frac{X_{V}}{X_{L}}$ 1.00 0.88 E_(BL) 1.001.00 ${E_{EFF}({calc})} = \frac{E_{A}}{E_{BL}}$ 1.00 0.88 MinimumEffective vaporization efficiency 0.9  0.9  Compare E_(EFF) and MinE_(EFF) 1.00 > 0.9 0.88 < 0.9

It should be appreciated that while a preferred embodiment of thepresent invention has been described with reference to determining anefficiency of vaporization for vaporized hydrogen peroxide, it iscontemplated that the present invention finds utility in determining anefficiency of vaporization for other chemical components. These chemicalcomponents may comprise decontaminating chemicals, including, but notlimited to, chemicals selected from the group consisting of:hypochlorites, iodophors, quaternary ammonium chlorides (Quats), acidsanitizers, aldehydes (formaldehyde and glutaraldehyde), alcohols,phenolics, peracetic acid (PAA), and chlorine dioxide.

Specific examples of decontaminating chemicals, include, but are notlimited to, hydrogen peroxide, peracids such as peracetic acid, bleach,ammonia, ethylene oxide, fluorine containing chemicals, chlorinecontaining chemicals, bromine containing chemicals, vaporized hydrogenperoxide, vaporized bleach, vaporized peracid, vaporized peracetic acid,ozone, ethylene oxide, chlorine dioxide, halogen containing compounds,other highly oxidative chemicals (i.e., oxidants), and mixtures thereof.

The decontaminating chemicals may also be combined with other chemicals.Examples of other chemicals that may be combined with decontaminatingchemicals, include, but are not limited to, water, de-ionized water,distilled water, an alcohol (e.g., a tertiary alcohol), aglycol-containing chemical compound, and mixtures thereof.Glycol-containing chemical compounds include, but are not limited to,polyethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, glycol ethers, polypropylene glycol, propyleneglycol, dc-ionized water vapor, distilled water vapor, a vaporizedalcohol (e.g., a tertiary alcohol), and mixtures thereof.

The foregoing description is a specific embodiment of the presentinvention. It should be appreciated that this embodiment is describedfor purposes of illustration only, and that numerous alterations andmodifications may be practiced by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is intendedthat all such modifications and alterations be included insofar as theycome within the scope of the invention as claimed or the equivalentsthereof.

1. A method for determining efficiency of a vaporizer for a vaporizationprocess, the method comprising the steps of: storing a plurality offirst data values in a memory, wherein said first data values areindicative of an electrical property of a capacitor in response to aplurality of predetermined concentrations of hydrogen peroxide in aliquid decontaminate, exposing a first sensor, having a capacitor, tothe liquid decontaminate including hydrogen peroxide, wherein theelectrical property of the capacitor is used to generate a first signalindicative of the concentration of hydrogen peroxide in the liquiddecontaminate before vaporization by a vaporizer; vaporizing the liquidto produce a gas including a vaporized decontaminate; and exposing asecond sensor to the gas, wherein the second sensor generates a secondsignal indicative of the concentration of vaporized hydrogen peroxide inthe vaporized decontaminate; determining concentration of hydrogenperoxide in the liquid decontaminate (X_(L)) using the first signal andsaid plurality of first data values; determining concentration of thevaporied hydrogen peroxide (X_(V)) using the second signal; anddetermining actual vaporization efficiency (E_(A)) according toE_(A)=X_(V)/X_(L).
 2. A method as defined in claim 1 further comprising:establishing a baseline efficiency (E_(BL)), wherein E_(BL) is apredetermined baseline efficiency for evaluating performance of saidvaporizer; and determining an effective vaporization efficiency(E_(EFF)) according to E_(EFF)=E_(A)/E_(BL).
 3. A method as defined inclaim 2, wherein said method further comprises: comparing the determinedeffective vaporization efficiency (E_(EFF)) to a predetermined value inorder to determine whether E_(EFF) is acceptable.
 4. A method as definedby claim 3, wherein said method further comprises: alerting an operatorto an unacceptable condition if E_(EFF) is not acceptable.
 5. A methodas defined by claim 1, wherein said liquid includes at least oneadditional chemical component, and said gas includes at least oneadditional chemical component.
 6. A method as defined in claim 1,wherein said first sensor is located in a conduit in fluid communicationwith a liquid decontaminate supply and said vaporizer.
 7. A method asdefined in claim 1, wherein said first sensor is located in a liquiddecontaminate supply for supplying liquid decontaminate to saidvaporizer.
 8. A method as defined in claim 1, wherein said second sensoris located in a conduit in fluid communication with said vaporizer and atreatment chamber.
 9. A method as defined in claim 1, wherein saidsecond sensor is located in said treatment chamber, said treatmentchamber receiving the vaporized decontaminate.
 10. A method as definedin claim 1, wherein said second sensor includes a piezoelectric devicehaving a material that interacts or is reactive with vaporized hydrogenperoxide.
 11. A method as defined in claim 1, wherein said methodfurther comprises storing a plurality of second data values in saidmemory, wherein said second data values are indicative of electricalresponses of the second sensor to a plurality of predeterminedconcentrations of vaporized hydrogen peroxide.